1. Field of the Invention
This invention relates to olefinically unsaturated polyisocyanates containing allophanate groups, to a process for their production and to their use as binders in one-component coating compositions.
2. Description of the Prior Art
One-component coating compositions based on NCO-functional urethane prepolymers are known (Houben-Weyl, Methoden der Organischen Chemie, Vol. E 20, page 1646, Georg Thieme Verlag 1987). They are prepared by reaction of diisocyanates or modified diisocyanates with polyols of relatively high functionality, such as polyether and polyester polyols. Their relatively high molecular weight structure provides these compounds with good film-forming properties and the resulting coatings with good optical properties. However, because they also have a relatively high viscosity, they can only be used as lacquer binders in heavily diluted form or in combination with a considerable amount of monomeric diisocyanate. However, high concentrations of monomeric isocyanate are physiologically unacceptable. In addition, the use of large quantities of solvent is ecologically unacceptable. The gap between a high molecular weight, high-functionality structure having a high viscosity, but resulting in excellent product properties on the one hand and low molecular weight, low-viscosity products with inadequate solvent resistance and inadequate drying properties on the other hand cannot be closed by NCO-functional prepolymers prepared as described above.
In addition to NCO-functional coating materials, one-component systems crosslinkable by oxidation have also been described (Ullmann, Enzyklopadie der technischen Chemie, 4th Edition, Vol. 19, pages 75 et seq., Verlag Chemie Weinheim, Deerfield Beach, Fla./Basel 1980). These systems also can only be used as binders for coating compositions in the form of dilute solutions.
Coating compositions which have both an oxidative drying mechanism and an isocyanate-crosslinking drying mechanism were previously unknown.
However, it has now surprisingly been found that olefinically unsaturated, allophanate polyisocyanates prepared from (cyclo)aliphatic polyisocyanates, preferably diisocyanates, and olefinically unsaturated, preferably monohydric alcohols represent interesting binders for one-component coating compositions which may be cured by oxidation and under the effect of moisture. These binders are particularly suitable for the production of solventless or low-solvent coating compositions having good lacquer properties, rapid chemical drying at room temperature and universal and physiologically safe usability.
Polyisocyanates containing allophanate groups are known, for example, from EP-A-0,000,194, EP-A-0,303,150 or GB-PS 994,890. Although olefinically unsaturated alcohols are also mentioned occasionally as starting materials in long lists of suitable alcohols, there is no specific reference to olefinically unsaturated allophanate polyisocyanates of the type according to the present invention and no specific reference to their use in one-component, oxidation- and moisture-curing coating compositions.
The allophanate polyisocyanates described in EP-A-0,524,500, EP-A-0,524,501 and EP-A-0,566,037 are not based on unsaturated alcohols and are recommended as crosslinking agents for two-component coating compositions.
Applicants' earlier German patent applications P 43 05 162.6 and P 43 14 252.4 relate to olefinically unsaturated isocyanates which may be used as binders in one-component coating compositions. However, these isocyanates are not polyisocyanates containing allophanate groups of the type according to the invention.